I just saw the extended edition of The Two Towers - the second part of The Lord of the Rings. It really works. It doesn't seem long and adds some useful additional storytelling. It does not however correct the poor treatment given to the subject of the Ents.
One of the sad things about a film of a book with as much potential for self-imagining as The Lord of the Rings is that one's own visual memories of the story are being supplanted by the now canonical imagery of the film. In this film that particularly affects the Ents. The treatment of the Ents was the only major disappointment when LOTR-TTT (no that's too geeky) The Two Towers came out. They were too smal and looked too much like people in the film. According to my imagination, they were not supposed to have legs, they just mysteriously moved about. The film does justice to the descriptions in the book, but not - in this particular case - to my imagination.
One of the problems with making a film of The Lord of The Rings is that a lot of the action is only described after the fact in rather distant third person narrative. An example of that is the capture of Isengard. In the book only the results are described. The Ents come off not so much as big tree-like men who can fight, but as some kind of sentient natural force that, once awakened, is irresistible. In the film it is just a fight between some very big guys and some slightly smaller guys, which takes away a lot of the Entish mystery. Finally, the Ents are not tricked by the hobbits into taking on Saruman, but decide so on their own. Again the film version reduces the impact of the Ents. Instead of being a race of powerful secretive beings, they are somewhat ridiculous tree-herders who can be tricked.